Select elements using

[MartinWa]

Hi!

I'm working with two meshes (bearing/shaft) and need to connect them using spring elements but I'm having problems both to select the correct elements and to make the spring.

1st: How do I select the correct elements. I've made a cylindrical coordinate system at the center of a bearing, using Tools->List I can select nodes at the correct position using this coord but I cant find out how to instead find the elements.

2nd: When creating a 1D spring element I can only specify one Application Region. Should I in this region specify both elements on the shaft and on the bearing? How does patran know how to connect the elements? Does it for each element select the closest element that is not connected otherwise?

 

[fl11]

Hi MartinWA,

A CELAS only connects two nodes together, not elements. The way define a CELAS in Patran, is to first creat a Bar element between two nodes. Once this element is created, you need to create a 1D propertie CELAS, give it the proper stiffness and then, for the application region, select the "bar" element you have created. The nodes being connected, the mesh will follow.

You should also have your meshes coincident as much as possible. Sometime, using CELAS on non-coincident nodes gives some strange results.

If there is any other way to connect meshes toghether using CELAS, I don't know it.

 

[MartinWa]

Thank you!

I managed to connect the meshes and run the analysis...

Tough it was a bit tricky to find out which nodes to connect. I had to export all locations of the interesting nodes to Excel and in that program I ran a little VB-script that told me which nodes are closest to eachother.

 

[Onda]

MartinWa,

To create the Gap elements You could use the Utility:
Utilities-->Fem-Elemnts-->Create 1D Gap Elements.
With this Utilities you could create Gap on all nodes that are within a certain tolerance.
Then You have to give to the bar the correct CElas property or You could use CBush elements if you prefer (1 element for 6 DOF instead of 6 elements for 6 DOF)!

Onda

 

[MartinWa]

Yep, that seems like a better solution (the GAP-finder ...

But now I have another problem, Patran doesn't seem to respect the Coordinate system I choose. When creating the springs I can also type in which coordinate system that my DOF is related to. This should be a cylindrical coord-system and I type in Coord 2 in the box. But when doing the anlysis the DOF of the spring is related to the global coordinate system (0) which is rectangular...

 

[Onda]

You should change the Analysis coordinate frame of the grids points.

Under Elements-->Modify-->Node-->Edit--> Analysis Coordinate Frame.

Remember that both nodes should have same Analysis coordinate system else results are not predictable.

Onda

 

[MartinWa]

Thank you again!

It's those little things that are easy once you know them but very hard to figure out on your own... =/